JS to reposition elements when they leave the viewport?

JavaScript
#1

I’m looking for a way to reposition elements on the bottom-right of the viewport once the elements are scrolled out of the viewport from their original position.

I can’t find an example at the moment, but this is common with video ads and also blog posts that have embedded video/audio players.

For example, suppose I have an embedded Youtube Video/Soundcloud. It’s positioned by default at the top of the page. But, once the the user scrolls down the viewport, after the media player element is

I’m a noobie, but the best thing I can come up with is to pass the height of the media player and then add the scroll listener to position:fixed the media player element once they’ve scrolled down enough.

What’s the best way to tackle this?

#2

You might look up a snippet of JS code for “lazy loading” images, as this is essentially the test in the opposite direction. It would give you a jump start on what you want to do. Basically, grab the bounding box around your video, see if it’s viewable on the screen, and if not, move it somewhere else.

#3

Hi @jeremy58, a more modern approach (no IE support, naturally) would be using an intersection observer; for instance, you might toggle a CSS class like so:

const observer = new IntersectionObserver(entries => {
  entries.forEach(entry => {
    entry.target.classList.toggle(
      '-is-leaving',
      entry.intersectionRatio < 1
    )
  })
}, { threshold: [0, 1] })

document
  .querySelectorAll('.player')
  .forEach(player => observer.observe(player))

If you just want to make the element sticky though, you might look into use position: sticky instead (no IE support, naturally).